"Man is born free and everywhere he is in chains." The opening sentence of Rousseau's The Social Contract not only summarises his entire philosophical system, it also proves how important he still is today.

Written in 1762, The Social Contract picks up where his Discourse on the Origin and Basis of Inequality Among Men left off, defining natural man as being free and happy and living in the forest. Rousseau explains how man went from this state of autonomy to the modern condition, dominated by inequality, dependency, violence and unhappiness. There were positive aspects to this process too, he admits, including the creation of families, the discovery of tools and technology, and the building of cities and social organisations. Unfortunately, this also gives way to what Rousseau called the "right of the strongest", where a reign of inequality destroys man's original state of happiness and freedom. Humanity becomes alienated, and the Discourse on Inequality ends unhappily in general war.

The Social Contract is an attempt to find a solution to this problem. For Rousseau, because of man's "perfectibility", the passage from a natural state to a social one is both an accident and necessary. Unlike animals, men are programmed to create and progress from one condition to the next. Rousseau discovers a way men can associate themselves with each other while maintaining their own individual freedom inside a social and political organisation. He calls that concept the "general will". Simply put, it is a form of association in which an individual alienates himself completely to the general will, and therefore regains his freedom in a political form. This of course has been criticised: some say it leads directly to dictatorship. Others, like Louis Althusser, say it is based on the premise that the people enter into a contract with nobody else but themselves – a logical impossibility.

However, Rousseau believed that in the form of the general will, the alienation of man would transform itself into freedom – this makes him nothing less than the inventor of modern dialectics, uniting the opposing concepts of nature (or freedom) and society (or contract), in their own opposition. All of Rousseau's philosophy is an attempt to find a solution to the problem of alienation. For Rousseau, the only thing that made humans different from animals is his free will, something constantly placed in danger whenever man enters into society.

As a revolutionary thinker, Rousseau understood that the general will, or the will of the people, should be sovereign – and that is the catch. It is here where we regain our freedom inside social organisation. Only the general will – general interest as opposed to private interest – guarantees man his autonomy. No society can be free unless individuals understand that the general will or general interest should prevail over their own individual one.

Rousseau also wrote of the emergence of machines and the rise of technology. He was the first to say that nature has limited resources and that we are putting our own survival in danger by over-exploiting it.

"Man is born free and everywhere is in chains." Centuries after that prophetic opening sentence, we should ask ourselves if we can afford to ignore Rousseau's warning, in a world dominated by flashing mobile phones and social media. Man may indeed be born free, but in the 21st century, the chains may be even harder to see.